function first_summand(CONSTS, plot_data)

    c     = CONSTS.c;
    k0    = CONSTS.k0;
    a     = CONSTS.a;
    d     = CONSTS.d;

    zeta = 0.3*d;
    m = 1;
    period = pi/(k0*a);
    dots_per_period = 100; % 200
    order = 3;
    q_high = 0.5*log(10)*order/(k0*zeta);
    q_vec = (0.0 : period/dots_per_period : q_high)';

    if (plot_data)
        fprintf('N=%d\n', size(q_vec, 1));
    end

    y_vec = - ((2*pi*k0^2*a)/c) * func_1(q_vec, zeta, m, CONSTS);

    if (plot_data)
        figure; plot(q_vec, y_vec); title('func_1');
    end

end